The term “delineation”, also referred to as “packet synchronization”, should be understood to mean the step consisting in determining, in a continuous data stream, the length of the packets and their limits, essential in reception.
The current delineation techniques require integrity of the data. When the link is not reliable enough, a transmission error correction step usually precedes the delineation. Furthermore, the current techniques demand, for example, the addition of information such as length information, pointers, in the payload that consumes bandwidth on the transmitted stream.
FIG. 1 is a schematic representation of a communication system implementing a delineation method according to the state of the art. The communication system comprises a transmission chain with, at the transmit end E, the formation of the transmitted stream FD, a communication channel C and, at the receiving end R, the processing of the received stream FE. In the transmit part, the stream is, for example, coded by a FEC coder then modulated. This stream FD is transmitted via the communication channel C then received by a recipient receiver R. Upon reception, the stream is demodulated and decoded by a FEC decoder 200. The delineation device 210 for the stream is placed after the transmission error correction function which, in this example, is handled by the FEC decoder. In practice, the FEC technique consists, for the sender, in adding redundancy to the payload in order to enable the recipient receiver to detect and correct some of the inevitable transmission errors.
In all cases, the existing techniques are based on the addition of control or redundancy data to the payload stream and delineation following the transmission error correction because this step requires integral data. Typical examples are the delineation in the cases of the MPE/MPEG2, ULE/MPEG2 or AAL5/ATM (Unidirectional Lightweight Encapsulation (ULE); Multi Protocol Encapsulation (MPE); ATM adaptation Layer (AAL5)) protocols.
The aim of the present invention is to remedy this drawback by proposing a non-intrusive, robust delineation solution that can be applied equally to an integral data stream and to a data stream including transmission errors, without the need to add data to the transmitted payload stream (i.e., neither redundancy nor control information).
In the case of a delineation step on an integral data stream, that is to say, at the level where the conventional mechanisms operate, the delineation according to the inventive method can be done without adding redundancy.
In the case of a delineation step on a data stream without transmission error correction, the delineation can also take place, because this step is, according to the invention, made independent of the need for data integrity. The packets of error-tolerant applications such as Voice-over-IP (VoIP) can be transmitted to the higher layers even if errors are present. The adaptation layers such as MPE, ULE or GSE (Generic Stream Encapsulation) can, with this method, have information to improve on delineation applied by a mechanism other than that of the present invention.